The present invention relates to safe and arming devices for explosive projectiles, and more particularly to safe and arming devices for spin stabilized projectiles in which the safe and arming device isolates the fuse from the main explosive charge of the projectile to prevent premature detonation of such projectile.
Generally, the function of a safe and arming device, as its name implies, is to insure and maintain a safe condition for the cannon shells or other types of explosive projectiles until it is desired that the shells be capable of being detonated, at which time the shells are armed. In other words, the safe and arming device serves to prevent premature detonation of the shell, generally, prior to and during loading of the shells into the cannon or other firing device and provides a meaningful safe separation distance, for protection of the launch crew, along the projectiles flight path subsequent to firing. For this purpose, the safe and arming device is placed between the fuse and the main explosive charge of the cannon shell or other type of explosive projectile, and serves to interrupt or prevent communication of a detonation signal from the fuse to the explosive charge. Only at such time that it is desired to be able to detonate the shell (such as for example, after it is fired) is the safe and arming device allowed to assume an armed position in which a detonation signal may be communicated from the fuse to the main explosive charge of the shell.
On spin stabilized projectiles, which rotate rapidly about the axis on the projectile upon firing, the safe and arming device generally comprises a mechanism which rotates into the armed position in response to the rotation of the shell. However, prior to 1950, safe and arming devices for mechanical time fuses used on spin stabilized cannon shells were only capable of providing enough time delay to insure that the cannon shell would not detonate within the gun tube. Thus, once the shell is fired, it could be immediately detonated upon impacting an object in the path of the shell, such as for example, tree branches, birds, etc. Such immediate detonation could in turn cause extensive damages and injury to the equipment personnel in the vicinity from which the shell was fired.
Consequently, a longer time delay was desired to allow the shell to travel a substantial distance from its firing point before it is capable of detonating. For example, safe and arming devices were developed which were capable of allowing the shell to travel over 200 feet before it was capable of detonating. However, such prior art safe and arming devices have used a plurality of small pinions and complicated gearing arrangements to provide such time delay to prevent premature detonation of the explosive projectile. Such gearing arrangements and especially the small pinions used therein, because of the necessity of maintaining tight tolerances, are quite expensive to manufacture and/or to assemble in the safe and arming housing.